1. Field of the Invention
The present invention relates generally to motion estimation, and more specifically to a programmable architecture and methods for motion vector and/or prediction error determination.
2. Description of Related Art
Applications such as video telephone, digital television, and interactive multimedia using such digital storage technology as CD-ROM, digital audio tape, and magnetic disk require digital video coding, or video compression, to achieve the necessary high data transfer rates over relatively low bandwidth channels. Various standards have been proposed for video coding. A standard for the storage and transmission of still images has been adopted by the International Standards Organization ("ISO"), Joint Photographic Expert Group ("JPEC"); see "JPEC Technical Specification, Revision 5," JPEG-8-R5, January 1980. A standard for digital television broadcast coding at 30/45 Mb/s is under consideration; see CCIR-CMTT/2, "Digital Transmission of Component-Coded Television Signals at 30-34 Mb/s and 45 Mb/s Using the Discrete Cosine Transform," Document CMTT/2-55. A standard for video telephony and video conferencing at 64 to 1920 kb/s has been adopted by the International Consultative Committee for Telephone and Telegraph ("CCITT"); see "Draft Revision of Recommendation H.261," Document 572, CCITT SG XV, Working Party XV/1, Spec. Grp. on Coding for Visual Telephony. A standard for storage applications below 1.5 Mb/s, which are similar to the applications targeted by the CCITT standard, is under consideration by the Moving Picture Experts Group ("MPEG") of the ISO. Video coding algorithms have been proposed as contributions to the standardization activity of ISO/MPEG; see Wong et al., "MCPIC: A Video Coding Algorithm for Transmission and Storage Applications," IEEE Communications Magazine, November 1990, pp. 24-32.
Many video coding techniques include a predictive mode that realizes data compression between two different video frames by identifying how a frame is unlike a preceding frame. In predictive mode, the frame is represented in terms of a set of vectors of the displacement of respective groups of pixels in the frame relative to their position in the preceding frame, known as motion vectors; and difference information representing the degree of difference between the displaced pixels and the corresponding pixels in the preceding frame. Because the amount of data in the set of motion vectors and difference information tends to be considerably less than the amount of data in the frame itself, the two frames are adequately represented by the considerably less data present in the preceding frame plus the motion vectors and difference information. When the frame is required in uncompressed form, it is reconstructed by applying the motion vectors and difference information to the preceding frame.
Because effective video coding requires the intimate integration of digital video compression technology, integrated circuit technology, and digital storage media, and as various standards for digital video compression exist and are proposed, a need has arisen for a flexible, high performance, low implementation cost programmable architecture for motion estimation.